The damaging effects of sunlight on skin are well documented. Much damage is due to routine day-to-day activities in the sunlight.
The major short term hazard of prolonged exposure to sunlight is erythema (i.e., sunburn). The 290 to 320 nanometer wavelength ultraviolet radiation range, designated as the "UVB" wavelength range, tends to be the primary cause of erythema. The 320 to 400 nanometer wavelength ultraviolet radiation range, designated as the "UVA" wavelength range, also produces erythema.
In addition to the short term hazard of erythema, there are also long term hazards associated with UV radiation exposure. One of these long term hazards is malignant changes in the skin surface. Numerous epidemiologic studies demonstrate a strong relationship between sunlight exposure and human skin cancer. Another long term hazard of ultraviolet radiation is premature aging of the skin. This condition is characterized by wrinkling and yellowing of the skin, along with other physical changes such as cracking, telangiectasis (spider vessels), solar keratoses (growths), ecchymoses (subcutaneous hemorrhagic lesions), and loss of elasticity (sagging). The adverse effects associated with exposure to UVA and UVB wavelength radiation are more fully discussed in DeSimone, "Sunscreen and Suntan Products", Handbook of Nonprescription Drugs, 7th Ed, Chapter 26, pp. 499-511 (American Pharmaceutical Association, Washington, D.C.; 1982); Grove and Forbes, "A Method for Evaluating the Photoprotection Action of Sunscreen Agents Against UV-A Radiation", International Journal of Cosmetic Science, 4, pp. 15-24 (1982); and U.S. Pat. No. 4,387,089, DePolo, issued Jun. 7, 1983. Hence, although the immediate effects of ultraviolet radiation may be cosmetically and socially gratifying, the long-term hazards are cumulative and potentially serious. include titanium dioxide and zinc oxide. However, these agents are very susceptible to rub-off or wear-off, resulting in little or no protection.
The most common agents for sun protection are sunscreens. These agents exert their effects through absorption of ultraviolet radiation so that it cannot penetrate the skin. Sunscreens must remain on the surface of the skin during exposure. However, sunscreens are easily rubbed off or washed off by sweating or swimming and can also be lost by penetration into the skin.
It is well-known that ultraviolet light induces inflammation of the skin and harmful photochemical reactions therein. During exposure and as repair of the UV damage takes place, super-oxide (O.sub.2.sup.-) radicals are formed in the skin. UV iradiation also causes some microvascular damage in the skin. This leads to local hemorrhage and "leakage" of blood cells into the dermis. Iron from the hemoglobin accumulates in the extra-cellular matrix of the tissue as Fe.sup.+2 and Fe.sup.+3. It is known that iron catalytically participates in the conversion of superoxide radicals to hydroxyl radicals, a species which is known to be very damaging to tissue.
It is an object of the subject invention to provide a topical composition, the use of which will prevent chronic (photoaging) effects of exposure to the sun.
It is also an object of the subject invention to provide a topical composition, the use of which will prevent acute (erythema) effects of exposure to the sun.
It is also an object of the subject invention to provide a topical composition for preventing the deleterious effects of the sun with minimal interference to the tanning response.
It is further an object of the subject invention to provide a photoprotective composition which penetrates into the skin and which has low susceptiblility to rub-off, wear-off or wash-off.
It is a still further object of the subject invention to provide a photoprotective composition which can be applied to the skin in advance of UV exposure without significant loss of efficacy.
It is also an object of the subject invention to provide a method for preventing the deleterious effects of the sun with minimal interference to the tanning response.